Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/366—Composites as layered products
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
  • Y10T428/2991—Coated

Definitions

• This invention relates to electrochemical cells and batteries, and more particularly, to improved electrode active material of such batteries, and novel methods of synthesis.
• Lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include an anode (negative electrode) , a cathode (positive electrode) , and an electrolyte interposed between spaced apart positive and negative electrodes. Batteries with anodes of metallic lithium and containing metal chalcogenide cathode active material are known.
• the electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous (aprotic) organic solvents.
• electrolytes are solid electrolytes typically called polymeric matrixes that contain an ionic conductive medium, typically a metallic powder or salt, in combination with a polymer that itself may be ionically conductive which is electrically insulating.
• an ionic conductive medium typically a metallic powder or salt
• the negative electrode of the cell is defined as the anode.
• Cells having a metallic lithium anode and metal chalcogenide cathode are charged in an initial condition.
• lithium ions from the metallic anode pass through the liquid electrolyte to the electrochemical active (electroactive) material of the cathode whereupon they release electrical energy to an external circuit.
• intercalation anode such as a lithium metal chalcogenide or lithium metal oxide.
• Carbon anodes such as coke and graphite, are also intercalation materials.
• Such negative electrodes are used with lithium- containing intercalation cathodes, in order to form an electroactive couple in a cell.
• Such cells in an initial condition, are not charged.
• In order to be used to deliver electrochemical energy such cells must be charged in order to transfer lithium to the anode from the lithium- containing cathode. During discharge the lithium is transferred from the anode back to the cathode. During a subsequent recharge, the lithium is transferred back to the anode where it reintercalates .
• lithium ions Li +
• Such rechargeable batteries having no free metallic species are called rechargeable ion batteries or rocking chair batteries. See U.S. Patent Numbers 5,418,090; 4,464,447; 4,194,062; and 5,130,211.
• Preferred positive electrode active materials include LiCo0 2 , LiMn 2 0 4 , and LiNi0 2 .
• the cobalt compounds are relatively expensive and the nickel compounds are difficult to synthesize.
• a relatively economical positive electrode is LiMn 2 0 4 , for which methods of synthesis are known, and involve reacting generally stoichiometric quantities of a lithium-containing compound and a manganese containing compound.
• the lithium cobalt oxide (LiCo0 2 ) , the lithium manganese oxide (LiMn 2 0 4 ) , and the lithium nickel oxide (LiNi0 2 ) all have a common disadvantage in that the charge capacity of a cell comprising such cathodes suffers a significant loss in capacity.
• the initial capacity available (amp hours/gram) from LiMn 2 0 4 , LiNi0 2 , and LiCo0 2 is less than the theoretical capacity because less than 1 atomic unit of lithium engages in the electrochemical reaction.
• Such an initial capacity value is significantly diminished during the first cycle operation and such capacity further diminishes on every successive cycle of operation.
• the specific capacity for LiMn 2 0 4 is at best 148 milliamp hours per gram. As described by those skilled in the field, the best that one might hope for is a reversible capacity of the order of 110 to 120 milliamp hours per gram.
• Capacity fading is well known and is calculated according to the equation given below. The equation is used to calculate the first cycle capacity loss. This same equation is also used to calculate subsequent progressive capacity loss during subsequent cycling relative back to the first cycle capacity charge reference.
• the present invention provides a composition suitable for use as an electrochemically active material for an electrochemical cell.
• the composition comprises particles of spinel lithium manganese oxide having on the surface of the particles ionic metal species bound to the spinel at oppositely charged respective ionic sites of the spinel particle surface.
• the ionic metal species preferably includes a transition metal.
• the ionic metal species includes a non-transition metal capable of a +3 valence state .
• the ionic species may contain mixtures of the foregoing metals.
• Cationic metal species bound to the spinel particle surface include, but are not limited to, metal cation, metal oxide cation, and metal phosphate cation.
• the composition comprising the spinel lithium manganese oxide having ionic species bound thereto is prepared by decomposing or melting a precursor metal compound on the surface of the spinel particles, thereby giving rise to the cationic metal species .
• the spinel lithium manganese oxide treated for improved results by the method of the invention is known to have the nominal formula Li 1 Mn 2 0 4 .
• Such spinel lithium manganese oxide compounds may vary in the relative proportion of lithium, manganese, and oxygen while maintaining identity as a spinel lithium manganese oxide insertion compound.
• the invention is not limited to any particular formulation for a spinel lithium manganese oxide.
• advantageous results are obtained when the spinel lithium manganese oxide is represented by the nominal formula Li 1+x Mn 2 .. x 0 4 where x is a range of about -0.2 to about +0.5; and more preferably where x is greater than zero and up to about 0.5.
• the treated spinel lithium manganese oxide is prepared as an electrode by mixing it with a binder and optionally with an electrically conductive material and forming it into an electrical structure.
• the composite spinel manganese oxide particles having the metal species bound thereto is prepared by first forming a mixture comprising the lithium manganese oxide particles and the metal compound.
• the mixture may be formed by mixing lithium manganese oxide powder and metal compound powder.
• the metal compound may be any suitable metal compound.
• metal salt (metal salt) is dissolved in a suitable solvent, then the lithium manganese oxide particles are thoroughly wetted by the solution before reaction. Reaction is conducted by heating the mixture containing the spinel particles and the metal compound for a time and at a temperature sufficient to form a decomposition product of the metal compound on the surface of the particles.
• the metal compound is reacted at the surface of the spinel while undergoing limited, very little, or no decomposition.
• the metal compound is a phosphate salt
• the phosphate salts retain their phosphate groups, and the heating serves to chemically disperse and adhere the phosphate to the spinel .
• the heating to cause reaction between the metal compound and the surface of the lithium manganese oxide be conducted at a temperature in a range from about 200°C to about 800°C, desirably 200°C to about 750°C, more desirably 200°C to about 700°C, in an air atmosphere for at least about 1/2 hour and up to about 6 hours. Since any amount of the metal compound will improve the characteristics of the LMO, there is no practical lower limit to the amount to be added as long as the amount is greater than zero. It is preferred that the amount of metal compound included with the lithium manganese oxide in the mixture be up to about 10 wt. % of the mixture with the lithium manganese oxide constituting the balance.
• Objects, features, and advantages of the invention include an improved electrochemical cell or battery based on lithium which has improved charging and discharging characteristics, a large discharge capacity, and which maintains its integrity during cycling. Another object is to provide a cathode active material which combines the advantages of large discharge capacity and with relatively lesser capacity fading. It is also an object of the present invention. to provide positive electrodes having active materials which operate with good performance over a relatively broad temperature range. Another object is to provide a method for forming cathode active material which lends itself to commercial scale production providing for ease of preparing large quantities .
• FIG 1 is an EVS (electrochemical voltage spectroscopy) voltage/capacity profile for a cell embodying the specially treated lithium manganese oxide (LMO) material of the invention in combination with a lithium metal counter electrode in an electrolyte comprising a mixture of ethylene carbonate and dimethyl carbonate and including a one molar concentration of LiPF 6 salt.
• the lithium manganese oxide based electrode and the lithium metal counter electrode are maintained spaced apart by a separator of glass fiber which is interpenetrated by the solvent and the salt .
• the conditions of cycling are ⁇ 10 mV, between about 3.0 and 4.4 volts, and the critical current density is less than or equal to about 0.08 mA/cm 2 .
• the treated LMO was prepared using lithium aluminum chloride in a weight proportion of 4% LiAlCl 4 and 96% LMO.
• Figure 2 is an EVS differential capacity plot for the cell as described in connection with Figure 1.
• Figure 4 contains an x-ray diffraction analysis of conventional, untreated LMO, as received from a vendor .
• Figure 5 is an EVS voltage/capacity profile for a cell containing lithium manganese oxide material treated with cobalt nitrate to provide the active material for a positive electrode of the invention in combination with a lithium metal counter-electrode in an electrolyte as described with respect to Figure 1 above.
• the conditions of the test are as described with respect to Figure 1 above.
• the treated LMO was prepared using a weight proportion of 4% cobalt nitrate and 96% LMO.
• Figure 6 is an EVS differential capacity plot for the cell as described in connection with Figure 5.
• Figure 7 is an EVS voltage/capacity profile for a cell containing lithium manganese oxide material treated with cobalt nitrate to provide the active material for a positive electrode of the invention in combination with a lithium metal counter-electrode in an electrolyte as described with respect to Figure 1 above.
• the conditions of the test are as described with respect to Figure 1 above.
• the treated LMO was prepared using a weight proportion of 5.3% cobalt nitrate and 96% LMO.
• Figure 8 is an EVS differential capacity plot for the cell as described in connection with Figure 7.
• Figure 9 is an EVS voltage/capacity profile for a cell containing lithium manganese oxide material treated with chromium acetate to provide the active material for a positive electrode of the invention in combination with a lithium metal counter-electrode in an electrolyte as described with respect to Figure 1 above.
• the conditions of the test are as described with respect to Figure 1 above.
• the treated LMO was prepared using a weight proportion of 4% chromium acetate and 96% LMO.
• Figure 10 is an EVS differential capacity plot for the cell as described in connection with Figure 9.
• Figure 11 is a diagrammic representation of a typical laminated lithium-ion battery cell structure.
• Figure 12 is a diagrammic representation of a typical multicell battery cell structure.
• the treated lithium manganese oxide of this invention is obtained essentially as a result of the thermal dispersion of a metal compound onto the surface of the lithium manganese oxide and preferably concurrently the decomposition of said metal compound on the surface. This is accomplished by heating the dispersed metal compound at an elevated temperature after the metal compound and the LMO have been brought into contact with each other. It is believed that the treated lithium manganese oxide (LMO) made in accordance with this invention differs fundamentally from the lithium manganese oxide known in the art. This difference is reflected in the treated lithium manganese oxide distinguished electrical chemical performance in a cell and also distinguished by the process by which the treated LMO is prepared.
• metal compounds or their mixtures can be used, and metal salts are preferred.
• One group of desirable metal compounds are transition metal compounds.
• Another group of desirable metal compounds are non- transition metal compounds which contain a metal capable of a +3 valence state, such as aluminum.
• Some representative examples of the metal compounds which can be suitably utilized in the practice of this invention include, for example, LiAlCl 4 (lithium aluminum chloride), nitrates, including A1(N0 3 ) 3 (aluminum nitrate), Cr 2 (OCOCH 3 ) 4 (chromium acetate), NiC0 3 (nickel carbonate), Co(N0 3 ) 2 (cobalt nitrate), CoC0 3 (cobalt carbonate) , and ZrOCl 2 (zirconium aluminum chloride) .
• LiN0 3 LiN0 3 , Co(N0 3 ) 2 , A1(N0 3 ) 3 , NiC0 3 .
• Desirable metal compounds are transition metals with nitrates, acetates, carbonates, and phosphates; and especially preferred are the nitrates; with cobalt nitrate being most preferred.
• LMO lithium manganese oxide
• a range of formulations may be used consistent with the basic lithium manganese oxide spinel of the nominal general formula LiMn 2 0 4 .
• the nominal general formula LiMn 2 0 4 represents a relatively narrow range of spinel lithium manganese oxide compounds (referred to as LMO) which have stoichiometry that varies somewhat in the relative proportion of lithium, manganese and oxygen, but still having the spinel structure. Oxygen deficient spinels are not favored here. Relatively lithium rich spinels are favored here.
• LMO spinel lithium manganese oxide compounds
• One desirable range of compositions is the spinel formula Li 1+x Mn 2 _ x 0 4 where 0 ⁇ x ⁇ 0.5.
• Lithium deficient spinels with x less than O i.e., -0.2 are also known.
• a spinel lithium manganese oxide had a surface area of 0.9 m 2 /g; average particle size of 30 microns; lithium content of 4.1%, corresponding to Li x 07 ; less than 1% impurities and lattice parameter of 8.22.
• Such lithium manganese oxide compounds must have a suitably high surface area and the ability to be coated with metal compound which is dispersed and decomposed thereon. It is desirable in the preparation of the treated LMO according to the invention, that the surface area of the LMO is between about 0.5 and 2.5 m 2 /g and that the range of composition would be lithium content of 1.02 ⁇ x ⁇ 1.10.
• a mixture containing the metal compound and the LMO is used.
• the mixture is prepared simply by mixing mechanically a powder form of the metal compound and a powder form of the LMO.
• the mixture can also be obtained by adding to the LMO a solution or suspension of the metal compound in a suitable solvent. Thereafter, the solvent is removed from the resulting mixture by heating, vacuum, simple evaporation, or other equivalent means known in the art.
• solvents that can be suitably used include, acetone and primary or secondary alcohols having one to seven carbon atoms .
• One particularly suitable solvent is methanol.
• the amount of metal compound is desirably from 0.1 to 10%, more desirably from 0.5 to 5%, and preferably 1 to 4% by weight of the mixture, with the LMO constituting the balance.
• the prepared mixture containing the metal compound and the LMO is subjected to heating.
• This heating step is carried out at a temperature high enough to initiate the thermal dispersion of the metal compound onto the surface of individual particles of the LMO.
• the temperature is also desirably high enough to at least partially decompose the metal compound at the surface.
• the temperature is high enough to essentially completely decompose the metal compound, leaving behind the positive cation of the metal which formerly constituted the metal compound.
• the extent of decomposition depends upon the metal compound used and the desired result. Metal phosphate compounds do not significantly decompose, but do appear to be bound at the spinel surface, and form a reacted product with the spinel at the surface.
• the heating temperature is below the temperature at which the LMO will be decomposed, and the heating temperature is below the melting point of the LMO. Heating is conducted for a duration of time sufficient to thermally disperse the metal compound onto the surface of the LMO, and as stated above, is preferably sufficient to at least partially decompose it. It is considered that complete decomposition is achieved when the only residual from the metal compound remaining on the surface is a metal cation which originated from the compound. The exceptional case being as per the phosphate example .
• the heating step is conveniently performed at a temperature in the range of about 200°C to about 850°C for a period of time from about 0.5 to about 12 hours. Desirably the heating is conducted at about 200°C to about 800 °C, more desirably 200°C to about 750°C, and most desirably at about 200 °C to about 700 °C. In one embodiment, the heating is conducted at a temperature in the range of about 400 to about 500°C and for a time of about 4 to 6 hours. The conditions depend, in part, on the metal compound used.
• the heating step can be conveniently conducted in a suitable atmosphere such as ambient air.
• the heating should be carried out for a time period sufficient to cause a surface-area-reducing effect on the LMO. It is believed that the greater the amount of the residual metal ion remaining after dispersion and decomposition, the greater will be the surface area reduction effect.
• Positive electrode active materials were prepared and tested to determine physical, chemical and electrochemical features . The results are reported in Figures 1 to 10. Typical cell configurations will be described with reference to Figures 11 and 12.
• a typical laminated battery cell structure 10 is depicted in Figure 11. It comprises a negative electrode side 12, a positive electrode side 14, and an electrolyte/separator 16 therebetween. Negative electrode side 12 includes current collector 18, and positive electrode side 14 includes current collector 22.
• An electrolyte separator film 16 membrane of plasticized copolymer is positioned upon the electrode element and is covered with a positive electrode membrane 24 comprising a composition of a finely divided lithium intercalation compound in a polymeric binder matrix.
• An aluminum collector foil or grid 22 completes the assembly.
• Protective bagging material 40 covers the cell and prevents infiltration of air and moisture.
• a multicell battery configuration as per Figure 12 is prepared with copper current collector 51, negative electrode 53, electrolyte/separator 55, positive electrode 57, and aluminum current collector 59. Tabs 52 and 58 of the current collector elements form respective terminals for the battery structure .
• the relative weight proportions of the components of the positive electrode are generally: 50- 90% by weight active material; 5-30% carbon black as the electric conductive diluent; and 3-20% binder chosen to hold all particulate materials in contact with one another without degrading ionic conductivity. Stated ranges are not critical, and the amount of active material in an electrode may range from 25-95 weight percent.
• the negative electrode comprises about 50-95% by weight of a preferred graphite, with the balance constituted by the binder.
• a typical electrolyte separator film comprises approximately two parts polymer for every one part of a preferred fumed silica.
• the separator film Before removal of the plasticizer, the separator film comprises about 20-70% by weight of the composition; the balance constituted by the polymer and fumed silica in the aforesaid relative weight proportion.
• the conductive solvent comprises any number of suitable solvents and salts. Desirable solvents and salts are described in USPN 5,643,695 and 5,418,091. One example is a mixture of EC:DMC:LiPF 6 in a weight ratio of about 60:30:10.
• Solvents are selected to be used individually or in mixtures, and include dimethyl carbonate (DMC) , diethylcarbonate (DEC) , dipropylcarbonate (DPC) , ethylmethylcarbanate (EMC) , ethylene carbonate (EC) , propylene carbonate (PC), butylene carbonate, lactones, esters, glymes, sulfoxides, sulfolanes, etc.
• the preferred solvents are EC/DMC, EC/DEC, EC/DPC and EC/EMC.
• the salt content ranges from 5% to 65% by weight, preferably from 8% to 35% by weight.
• any number of methods are used to form films from the casting solution using conventional meter bar or doctor blade apparatus. It is usually sufficient to air-dry the films at moderate temperature to yield self-supporting films of copolymer composition.
• Lamination of assembled cell structures is accomplished by conventional means by pressing between metal plates at a temperature of about 120-160°C. Subsequent to lamination, the battery cell material may be stored either with the retained plasticizer or as a dry sheet after extraction of the plasticizer with a selective low-boiling point solvent.
• the plasticizer extraction solvent is not critical, and methanol or ether are often used.
• Separator membrane element 16 is generally polymeric and prepared from a composition comprising a copolymer.
• a preferred composition is the 75 to 92% vinylidene fluoride with 8 to 25% hexafluoropropylene copolymer (available commercially from Atochem North America as Kynar FLEX) and an organic solvent plasticizer.
• the plasticizing solvent may be one of the various organic compounds commonly used as solvents for electrolyte salts, e.g., propylene carbonate or ethylene carbonate, as well as mixtures of these compounds.
• Higher-boiling plasticizer compounds such as dibutyl phthalate, dimethyl phthalate, diethyl phthalate, and tris butoxyethyl phosphate are particularly suitable.
• Inorganic filler adjuncts such as fumed alumina or silanized fumed silica, may be used to enhance the physical strength and melt viscosity of a separator membrane and, in some compositions, to increase the subsequent level of electrolyte solution absorption.
• a current collector layer of aluminum foil or grid is overlaid with a positive electrode film, or membrane, separately prepared as a coated layer of a dispersion of intercalation electrode composition.
• This is typically an intercalation compound such as LiMn 2 0 4 (LMO) , LiCo0 2 , or LiNi0 2 , powder in a copolymer matrix solution, which is dried to form the positive electrode.
• An electrolyte/ separator membrane is formed as a dried coating of a composition comprising a solution containing VdF:HFP copolymer and a plasticizer solvent is then overlaid on the positive electrode film.
• a negative electrode membrane formed as a dried coating of a powdered carbon or other negative electrode material dispersion in a VdF:HFP copolymer matrix solution is similarly overlaid on the separator membrane layer.
• a copper current collector foil or grid is laid upon the negative electrode layer to complete the cell assembly.
• the VdF:HFP copolymer composition is used as a binder in all of the major cell components, positive electrode film, negative electrode film, and electrolyte/separator membrane.
• the assembled components are then heated under pressure to achieve heat-fusion bonding between the plasticized copolymer matrix electrode and electrolyte components, and to the collector grids, to thereby form an effective laminate of cell elements .
• This produces an essentially unitary and flexible battery cell structure.
• the electrochemical cell which utilizes the novel solvent of the invention may be prepared in a variety of ways.
• the negative electrode may be metallic lithium.
• the negative electrode is an intercalation active material, such as, metal oxides and graphite.
• the components of the electrode are the metal oxide, electrically conductive carbon, and binder, in proportions similar to that described above for the positive electrode.
• the negative electrode active material is graphite particles.
• test cells were fabricated using lithium metal electrodes. When forming cells for use as batteries, it is preferred to use an intercalation metal oxide positive electrode and a graphitic carbon negative electrode.
• Various methods for fabricating electrochemical cells and batteries and for forming electrode components are described herein. The invention is not, however, limited by any particular fabrication method as the novelty lies in the treated LMO active material .
• treated lithium manganese oxide was prepared using a lithium aluminum chloride compound.
• the lithium manganese oxide in this example had the nominal formula Li x .08 Mn ⁇ - 92 ° 4 anc ⁇ was obtained from Japan Energy Corporation.
• the lithium aluminum chloride had the formula LiAlCl 4 . It was obtained from Aldrich Chemical Company.
• the lithium aluminum chloride is known to be hygroscopic. This required that the grinding of the lithium aluminum chloride powder to the desired particle size be done under argon. The milled lithium aluminum chloride and the lithium manganese oxide powders were mixed and milled together to achieve a well intermingled mixture. The objective is to achieve an intermingled mixture which is as close to homogeneous as possible.
• the mixture constituted 4% by wt . of the lithium aluminum tetrachloride and 96% by wt . of the lithium manganese oxide.
• the intermingled particles were then heated in a furnace at a temperature of about 450°C for a time of about 1 hour. The heating was conducted in air, and no special atmosphere was required. Heating at this temperature and time was found to be sufficient to decompose the lithium aluminum chloride compound. After heating for 1 hour, the product was allowed to cool. The rate of cooling did not appear to be critical and it was possible to simply remove the product from the oven and let it cool down to room temperature. It is also possible to allow it to cool in the oven once the heat has been turned off. Quenching by cooling at room temperature is convenient but does not appear to be critical.
• the electrolyte was a 2 to 1 weight ratio of EC and DMC solvents and contained 1 molar LiPF 6 type salt .
• the separator was a glass fiber type.
• the counter electrode was metallic lithium.
• the current density of the test cell was 0.08 milliamp hours per cm 2 .
• test cell was based on 2.4 cm 2 positive electrode with active material loading of about 34 to 36 milligrams per cm 2 .
• the capacity was determined under constant current cycling + 0.08 mA/cm 2 at room temperature.
• the cell was cycled between about 3 and about 4.3 volts with performance as shown in the Figures .
• Figure 1 shows a voltage profile of the test cell, based on the treated lithium manganese oxide (LMO) positive electrode active material of the invention, and using a lithium metal counter electrode as described in the examples.
• the data shown in Figure 1 is based on the Electrochemical Voltage Spectroscopy (EVS) technique. Electrochemical and kinetic data were recorded using the Electrochemical Voltage Spectroscopy (EVS) technique.
• EVS Electrochemical Voltage Spectroscopy
• Such technique is known in the art as described by J. Barker in Synth, Met 28, D217 (1989); Synth. Met. 32, 43 (1989); J. Power Sources, 52, 185 (1994); and Electrochemical Acta, Vol. 40, No. 11, at 1603 (1995).
• FIG. 1 clearly shows and highlights the very good performance and reversibility of the treated lithium manganese oxide of the invention.
• the positive electrode contained about 85 milligrams of the treated active material.
• the total electrode weight including the binder and conductive carbon diluent was about 98 milligrams .
• the positive electrodes showed a performance of about 131 milliamp hours per gram on the first discharge. This means that the electrode provided a specific capacity of 131 milliamp hours per gram out (lithium extracted) .
• the order of 123 milliamp hours per gram was observed in (lithium inserted) .
• good performance continued to be exhibited.
• the positive electrode provided 130 mAh/gm on first discharge (lithium extracted) and 122 mAh/gm on the second cycle discharge.
• Figure 2 is an EVS differential capacity plot based on Figure 1.
• the relatively symmetrical nature of the peaks indicates good electrical reversibility, there being no peaks related to irreversible reactions, since all peaks above the axis (cell charge) have corresponding peaks below the axis (cell discharge) , and there is essentially no separation between the peaks above and below the axis .
• the peaks also show an indication of good crystallinity from their sharp appearance demonstrating a good crystallinity of the active material.
• Figure 3 shows the results of an x-ray diffraction analysis of the treated lithium manganese oxide prepared according to the invention.
• the x-ray diffraction was conducted using CuK ⁇ . type radiation.
• the diffraction analysis shown in Figure 3 is nearly identical to conventional lithium manganese oxide ( Figure 4) of the nominal formula Li 1 Mn 2 0 4 except for the presence of the added metal compound and some variations in the amount of lithium. This minor variation in the amount of lithium is within the variation expected when conventional lithium manganese oxide is prepared.
• Figure 4 shows that the structure of the treated LMO of the invention is similar, and essentially identical to, the basic spinel structure of conventional Li-Mn 2 0 4 .
• FIG. 4 contains an x-ray diffraction analysis of conventional lithium manganese oxide (Li 1 Mn 2 0 4 ) prepared according to conventional techniques and as received from the vendor. See USPN 5,770,018, incorporated by reference herein in its entirety, for a description of conventional LMO.
• the product of the invention has the same spinel structure as the conventional lithium manganese oxide, except that the product of the invention has the metal added to its surface.
• the a-axis parameter of the spinel product of the invention is 8.2330. This further demonstrates its similarity to conventional lithium manganese oxide having a similar a-axis parameter. Since this is a cubic structure, the other axes correspond and are all 90 degrees with respect to one another. These features are the same as conventional lithium manganese oxide.
• Example 2 97:3 LMO:LiAlCl, The procedure of Example 1 was followed except that the weight percent of the lithium manganese oxide and the lithium aluminum chloride were changed. In this example, 3% by wt . lithium aluminum tetrachloride was used and 97 wt. % lithium manganese oxide was used. As shown in Table 2, this example provided a slightly increased amount of lithium, but the cell parameters and peaks essentially remained unchanged. Here cycling performance was also good.
• Example 3 98:2 LMO: LiAlCl, The method of Example 1 was followed except that 2 wt . % lithium aluminum tetrachloride was combined with 98% lithium manganese oxide which was then heat treated in the manner as described with respect to Example 1. With reference to Table 2, it can be seen that the atomic amount of lithium present in this product was slightly increased compared to the prior examples since a lesser amount of the metal compound was used.
• Example 4 99:1 LMO:LiAlCl,
• Example 2 The method of Example 1 was followed except that the metal compound was cobalt phosphate.
• the metal compound was cobalt phosphate.
• cobalt phosphate was combined with the aforesaid conventional lithium manganese oxide obtained from the vendor. Heating was conducted at a temperature of about 200 °C for about 2 hours time. Good cycling performance was demonstrated.
• the spinel structure was also maintained when the metal compound used was cobalt phosphate .
• Example 6 A1(N0, ; 4 Wt. and 2.36 Wt. %
• Example 1 The method of Example 1 was followed except that the metal compound added to the lithium manganese oxide was aluminum nitrate.
• two formulations were prepared. One formulation contained 4% by wt . aluminum nitrate and 96% by wt . lithium manganese oxide. The other formulation contained 2.35% by wt . aluminum and the balance lithium manganese oxide.
• the two powders were heated together as per the same method as described with respect to Example 1, and heating was conducted at a temperature of 450 °C for about 2 hours. Reasonably good cycling performance was demonstrated and the spinel structure was maintained.
• Another batch at 4% was made and the surface area was 2.1 (again very high) . It seems likely that Al having a 3+ valence makes additional oxide; compared to the transition metals with 2+ as the preferred valence.
• Example 7 Cr 2 (OCOCH 3 ) , ; 3.08 Wt. % and 2.04 Wt . %
• Example 2 The method of Example 1 was followed except the metal compound used was chromium acetate.
• Two formulations were prepared. One contained 3.08 wt . % chromium acetate, the balance lithium manganese oxide; and the other contained 2.04 wt. % chromium acetate with the balance lithium manganese oxide. Each formulation was heated to about 450 °C for about 4 hours time to disperse the chromium compound on the particles of the lithium manganese oxide and to achieve decomposition of the chromium acetate thereon. As can be seen from Table 2, the surface area was considerably reduced. Cell performance was reasonably good. (See Figures 9 and 10) .
• Example 8 NiC03 ; 3.06 Wt. % and 2.04 Wt . %
• the method of Example 1 was followed except the metal compound used was nickel carbonate.
• Two formulations were prepared. One contained 3.06 wt. % nickel carbonate, the balance lithium manganese oxide; and the other contained 2.04 wt. % nickel carbonate with the balance lithium manganese oxide. Each formulation was heated treated to disperse the nickel compound on the particles of the lithium manganese oxide and to achieve decomposition of the nickel carbonate thereon. As can be seen from Table 2, cell performance was reasonably good.
• Example 9 Co(N0 3 ) 2 ; 5.30, 4.00, 10, and 3.00 Wt. %
• Example 2 The method of Example 1 was followed except the metal compound used was cobalt nitrate.
• Four formulations were prepared, respectively containing 5.30, 4.00, 10, and 3.00 wt % cobalt nitrate, and the balance lithium manganese oxide, respectively. Each formulation was heated treated to disperse the cobalt compound on the particles of the lithium manganese oxide and to achieve decomposition of the cobalt nitrate thereon. As can be seen from Table 2, cell performance ranged from good to very high capacity. One test revealed positive electrode performance of 137 mAh/g on first discharge (lithium out) and on subsequent cycling good performance was also observed. X-ray data for the 3 wt . % cobalt carbonate/97 wt . % LMO treated sample revealed 8.2144 angstrom lattice parameter consistent with the conventional spinel. (See Figures 5-8) .
• Example 1 the method of Example 1 was followed except that heating was conducted at different temperatures using a rotary oven (tube furnace) , and the constituents heated were as stated in Table 3.
• the cationic metal species which remain after decomposition of the metal compound provide metal -containing cations bound to the oxygen of the lithium manganese oxide at the surface of the lithium manganese oxide. This is different from forming a simple metal oxide layer over the surface.
• the cationic metal species which remain after decomposition of the metal compound are not thought to simply remain on the LMO surface as positively charged ions because as such they would leave during extraction of lithium during cell operation upon subsequent activation of the cells. Instead, the positively charged ions are thought to be incorporated into, in or on the outside layer of the spinel structure.
• the preferred metals are first row transition metals such as titanium (Ti) , vanadium (V) , chromium (Cr) , manganese (Mn) , iron (Fe) , cobalt (Co) , nickel (Ni) , copper (Cu) , and zinc (Zn) . These metals are thought to form ions which coordinate well with the oxygen at the surface of the spinel because they have a size roughly comparable to the Mn.
• Some second row transition metals may also be included and are selected from zirconium (Zr) , molybdenum (Mo) , palladium (Pd) , cadmium (Cd) , tungsten (W) , and platinum (Pt) .
• other non-transition-metal metals are used.
• metals capable of a +3 valence state such as aluminum.
• Other metals such as tin are also possible .
• the metal compound is a salt.
• the anion is the component which is driven off by heat.
• anions are usable to provide decomposition of the compound at temperature ranges described herein. Examples include chlorine, carbonate, and nitrate.
• the metal is dispersed preferably uniformly on the surface of the spinel, and reduces the surface area. In an optimized condition, the remaining metal provides an essentially complete coating to provide as low a surface area as possible. However, excess deposited metal or metal species is undesirable because the added weight adversely affects the specific capacity of the cathode active material.
• a metal salt preferably a transition metal salt, that melts or essentially reacts in the presence of the LMO to achieve decomposition at a preferred temperature of about 400°C to about 500°C.
• the metal to some extent goes down on the outer layer of the spinel crystal attached to an oxygen of the outer layer of the spinel at the terminals of lattice where the spinel ends in alternating two oxygens and one manganese. It is thought that the most likely place for the metals to attach is to the terminal oxygens of the lattice as evidenced by the fact that it is not possible to simply rinse away the metal cations after their deposition thereon from decomposition of the metal compound. If the metal cation were merely a plain ion, it would be possible to simply rinse it off.
• the anion of the metal compound is important only to the extent that the compound itself must be decomposable at a temperature below which the original spinel starts losing oxygen or the lithium becomes too mobile. Therefore, the lower the temperature at which the anion portion decomposes, the more attractive is its use.
• Metal compounds which are metal oxides are known to be very stable and only decomposable at very high temperatures on the order of 900°C.
• the compound decomposes at a temperature less than 900°C, desirably less than 800°C, more desirably less than 750°C, most desirably less than 650°C, and preferably less than 600 °C. More preferably the metal compound decomposes at a temperature less than 550°C.
• Some metal compounds are even capable of decomposing at a temperature as low as about 300°C to about 350 °C.
• a decomposition temperature in a range of about 400°C to about 500°C is suitable.
• the metal compounds, for use in the invention may be pre-screened by determining their melting point, their decomposition temperature, and by conducting thermal gravimetric analysis (TGA) .
• the carbonate anion would decompose leaving only the nickel.
• the effect of the depositing of metal cations on the surface of the LMO is reduced surface area which results in less corrosion of the manganese and better cycling.
• corrosion of the manganese it is meant that, manganese ions are oxidized and can eventually dissolved away during operation of the battery to the harsh conditions of battery operation.
• the addition of the metal cation of the invention has the beneficial effect of reducing corrosion of the manganese.
• the treated lithium manganese oxide of the invention is characterized by having extra capacity which seems to cause the ability to access more of the lithium or operation of the battery.
• the lithium carbonate decomposed at a temperature as low as about 650 °C, showing that decomposition of the metal compound is altered by the presence of the starting material LMO spinel .
• the metal cations at the surface are clearly not a metal coating and they somehow combine with the surface charge or atomic bonding, or ionic complex with the lithium manganese oxide. Therefore, the result is a decomposition product of the metal compound that forms in the presence of the LMO and after such decomposition reaction, the surface of the LMO loses some of its porosity. Under a scanning electron microscope (SEM) LMO particles treated with aluminum nitrate looked essentially polished demonstrating the surface area was lowered.
• SEM scanning electron microscope
• the metal compound acts as a fluxing agent while the decomposition reaction is ongoing because some of the gases given off during decomposition uniquely polish the surface of the LMO.
• a chlorine or nitrate compound chlorine or nitric oxide gas is given off as a reaction occurs, which reduces the terminal groups, the bound water and causes other related results. Therefore, decomposition gases reduced the terminal groups and the bound water within or on the spinel itself.
• the preferred anions in the metal compound are those that work best as flux agents. This means they have a greater mobility to move through and affect any porosity of the particles. This mobility also results in covering as much of the free surface area as possible to cause a surface reduction effect. It is evident that it is desirable to drive decomposition reaction to essentially full completion.
• metal cation of the metal compound effectively assumes a desired oxidation state for being maintained at the surface of the LMO while the reaction is conducted simply in air.
• Enhanced oxygen content may be beneficial, however, an oxidizing air environment was adequate.
• Another advantageous feature of the method of the invention is that the rate of heating and the rate of cooling do not appear to be critical. However, it is preferred that the synthesis be conducted at less than 600°C. Therefore, it is possible to simply heat the metal compound and the LMO in an oven and at the desired temperature for the desired amount of time and then permit it to cool. The added metal results in a small dilution effect with respect to the atomic weight proportion of the lithium.
• the amount of lithium initially is expected to vary between Li x Mn 2 0 4 , where x is 1.02 to 1.08.
• the atomic proportion of lithium in the final treated product will be lessened. If the metal compound itself contains lithium the atomic proportion of lithium and the final product will vary slightly depending on the relative weight of the lithium and other metal cations in the added metal compound.
• the methods of the invention it is possible to achieve the beneficial aspects of enhanced capacity, reduced loss of capacity during cycling, reduced surface area, and stabilizing of the LMO against corrosion, without changing the basic spinel structure of the original LMO compound as evidenced by no major shifts in the x-ray pattern of the treated LMO as compared to the untreated LMO.
• This is thought to be because the added metal produces a passivation layer around the LMO particles to provide stability.
• the manganese alone is not able to produce such a passivation layer. This distinguishes the lithium manganese oxide from other metal oxides such as lithium cobalt oxide and lithium nickel oxide which are known to be capable of producing a passivation layer.
• the methods of the invention are different from other approaches to attempting to improve performance of the LMO.
• the most common approach is to attempt to sinter the LMO at high temperature to achieve a more crystalline product by heating to about 800°C.
• the method of the present invention avoids sintering which has certain disadvantages including oxygen depletion.
• the present method also avoids forming Li 2 Mn0 3 which has been here found to be undesirable because of delithiation instabilities during discharge.
• the amount of additive metal compound necessary to achieve the beneficial results is not large.
• the amount added is determined by the amount of surface area reduction desired and the amount effective to essentially polish the surface and plug the porosity and to stabilize against corrosion. Therefore, a surface-area-reducing amount is all that is required.
• metal compound additions on the order of 5 wt . % resulting in on he order of 2 wt . % metal deposited on the surface provided surface reduction effect on the order of 20-30%. Further optimization is a matter of choice. It is thought that metal compound additions greater than about 10 wt. % resulting in deposited metal on the order of 4 wt . % is the maximum amount desirab1e .
• metals and preferably transition metals, are used to stabilize the crystal structure of the spinel.
• This surface treatment lowers the surface area of the LMO and improves high temperature performance.
• the capacity was increased each time.
• the resulting materials approach the theoretical capacity of nominal Li 1 Mn 2 0 4 at 140 milliamp hours per gram. This is particularly significant since all LMO with high capacity (or lithium content x approaching 1) suffer from very significant capacity fading during cycling even at room temperature.
• the LMO material treated with metal salts and preferred transition metal salts of the invention have demonstrated the benefit of high capacity and small capacity fade even at high temperature cycling at about 60 °C.
• the treated LMO is prepared by heating a mixture of LMO and a metal compound for a period of time and at a temperature sufficient to cause interdiffusion of excess lithium from the LMO spinel, and metal cation from the metal compound, into an interfacial layer thereby creating a new compound of spinel-like structure, possessing reduced surface area, increased capacity, and improved thermal stability.
• the heating is preferably conducted to cause complete reaction of the metal compound into the surface of the spinel, allowing for the interdiffusion of excess lithium from the spinel into the newly formed surface, thereby creating an improved spinel-like structure having the advantages stated above.
• the metal compound powder and the lithium manganese oxide powder may be mixed together as solids and then reacted.
• the metal salt can be dissolved in a suitable solvent, and the LMO thoroughly wetted by the solution before reaction to ensure near homogeneous dispersion of the additive.
• the reaction may be conducted in ambient air.
• the atmosphere does not need to be oxygen enriched at the temperatures described here, but inert atmosphere is not recommended.
• the metal compounds are preferably selected to decompose at a temperature less than 850°C, desirably less than 800°C, more desirably less than 750°C and to melt at temperatures less than those stated immediately earlier.
• Other metal compounds, with higher melting points and/or decomposition temperatures are still able to react with LMO at or below the immediately preceding temperatures and they react at the lower temperatures described herein.
• the criterion is reaction with the spinel at temperatures less than 850°C, desirably less than 800°C, more desirably less than 750°C, by melting and/or decomposing in the presence of the spinel LMO.
• the preference is to cause reaction at a temperature which does not cause spinel oxygen deficiency to become a problem.
• reaction with phosphate salts did not produce any measurable oxygen deficiency, that is, less than 0.01%.
• the decomposition product is primarily the metal cation. This will bond to the spinel structure via the terminal oxygens of the spinel .
• the terminal oxygen is usually attached to a proton (O-H group) . This is the most likely position of the metal cation, that is, replace the proton.
• the metal species can include both the metal cation and an additional oxygen atom.
• not all additives decompose completely to the metal cation.
• the phosphate salts retain their P0 4 groups. The end effect is lowered surface area of the treated spinel, improved capacity, and improved high temperature cycling.
• the temperature needed for the decomposition synthesis described here is advantageously relatively low, at 600°C or less.
• the lower decomposition synthesis temperature eliminates or significantly reduces the occurrence of oxygen deficiency and/or the production of Li 2 Mn0 3 .
• Oxygen deficiency is considered a crystal defect and to be avoided in spinel synthesis.
• Impurities such as Li 2 Mn0 3 appear prone to decomposition in electrolytes typically used in lithium polymer batteries. Impurities in cells have proven to shorten the life especially during operation at temperatures above ambient .

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